interface A {
   double f(double x,double y);
}
class B implements A {
   public double f(double x,double y) {
      return x*y;
   }
   int g(int a,int b) {
      return a+b;
   }
}
public class E1 {
public static void main(String args[]) {
   A a = new B();
   System.out.println(a.f(3,5));
   B b = (B)a;
   System.out.println(b.g(3,5));
 }
}
